1. Field of the Invention
The present invention is generally in the field of semiconductors and electronic devices. More specifically, the invention is in the field of bulk acoustic wave filters.
2. Background Art
Devices utilizing radio frequencies typically include filters, such as bulk acoustic wave (BAW) filters, in order to filter away unwanted signals, to prevent signal interference, or to eliminate noise. In such applications where BAW filters are used, it is desirable for the input signals allowed to pass through each BAW filter to be provided at the output of the BAW filter without distortion. However, when high power input signals are provided to a BAW filter, the BAW filter may produce a large amount of spurious output signals that may be unacceptable for some strict communication standards, such as the Universal Mobile Telecommunications System.
These spurious output signals typically result from nonlinearities, such as nonlinear elastic coefficients, nonlinear dielectric constants, and nonlinear piezoelectric constants existing in the individual BAW resonators used in the BAW filter. These nonlinearities, therefore, can cause the BAW resonators to generate undesirable harmonic signals which can cause the BAW filters to output spurious signals having twice the driving frequency and result in other types of nonlinear responses such as intermodulation distortion. Moreover, since BAW filters are typically designed using only a linear model, such spurious output signals cannot be predicted and minimized for proper BAW filter operation.
Accordingly, there is a need in the art for a bulk acoustic wave filter that minimizes undesirable harmonic signals to reduce the output of spurious signals. There is also a need for a robust methodology for designing such a filter.